RTX51 Tiny & "Timer 1" quandary

Basics:

When I attempt to enable Timer 1, RTX51 Tiny no longer will task swap.

Details:

- RTX51 Tiny running in Round-Robin Mode utilizes Timer 0
- Attempting to implement use of UART0 utilize Timer 1 as baud-rate generator as soon as Timer 1 is enabled, RTX no longer executes normal task swapping

Timer 1 initialization:


    // Turn Timer 1 OFF
    // --------------------
    TR1=0;

    // Disable pertinent interrupts
    // --------------------
    ET1=0;              // DISABLE_TIMER_1
    ES0=0;              // DISABLE_SERIAL_0_INT;

    // Define timer 1 mode
    // --------------------
    TMOD = ( 0x20 | (TMOD & 0x0F) ); // retain definition of Timer 0
                                    //  then define Timer 1
                                                // .7: Gate=0b: T/C enabled when TR1=1
                                    // .6: C/T_=0b: timer clkd by internal clk
                                    // .[5:4]: Mode=10b: 8-bit auto-reload
                                    //      timer for baud generation.
                                    // .[3-0]: Timer 0 defs

    // Configure Timer 1 for baud rate generation:
    // -------------------------------------------
    //  Crystal Frequency:  36.864 MHz
    //  Timer 1:  Mode 2, SMOD=0
    //  TH1 = 0xEC delivers 4800 Baud with 0% deviation
    TH1  =
    TL1  = 0xEC;                    // Timer 1 reload values

    PCON &= 0x3F;                   // PCON.[7:6] = SMOD0:SMOD1 = 0
                                    //  No baudrate doubling for UART0 or UART1

    // turn serial port on
    // --------------------
    // Port 0:
    SCON0   = 0xE0;         // 1110 0000: mode 3:  asynch, 11 bits, 1 stop,
                            //                     1 start, (Even) Parity
                            // SCON0.7: SM0     1: (mode 3:  asynch, 11 bits,
                            // SCON0.6: SM1     1:  timer 1 or 2 baud rate equation)
                            // SCON0.5: SM2     1: RI active when 9th bit = 1
                            // SCON0.4: REN_0   0: UART reception disabled (for now)
                            // SCON0.3: TB8_0   0: 9th transmission bit
                            // SCON0.2: RB8_0   0: 9th data bit that was received
                            // SCON0.1: TI_0    0: Transmit Interrupt flag.
                            // SCON0.0: RI_0    0: Receive Interrupt flag.

    // turn individual interrupts on
    // --------------------
    ET1=1;                              // ENABLE_TIMER_1_INT
    ES0=1;                              // ENABLE_SERIAL_0_INT

    // Turn Timer 1 ON
    // --------------------
    ET1=1;                              // ENABLE_TIMER_1

Results:
After the ET1=1 is executed, the 2nd task of a total of 2 tasks never goes READY and the system stays in the boot task.
I can't detect any where in this timer initialization code that could impact the RTX environment.

Can you detect something that is obvious that I'm overlooking?