I just checked that Tx-enable is high when Bootloading happens with UART V2.50 with PSoC4L.Just tried bootloading Bootloader_1 image.
Attaching the project.
sorry for the late response.
Yes - the TX_EN is permanent high while downloading. But that's wrong. Only when PSoC is sending something the TX_EN must be high. Please have a closer look to the attached JPG "Step3_RS485_FWU_with_emulated_TXEN.jpg". Channel 00 "RX" is payload of the PC. Channel 01 "TX" are answers of the PSOC. Channel 02 "TX_EN" is the PSoC Tx-enable pin of component UART component V2.50. Channel 03 "SIM_TX_EN" is a generated TX_EN signal with glue-logic.
Now - while bootloading channel 02 must look like channel 03. When you bootload over a RS-232 transceiver (e.g. MX202) you don't notice that cause you don't need the TX_EN pin anyway and the bootloading will work.
But when you bootload over a RS-485 transceiver (e.g. SN65HVD22D) the TX_EN pin of the component must work proper.
Please refer to the component datasheet PG 50, regarding the behaviour of TX_EN , in the project ,I'm seeing the same as well.So kindly try probing in the attached project and let us know what Tx_En probed signal.It is high as along as transmission occurs.