Excellent catch !
I took a peak at the corresponding portion of the BITX40 schematic and C114 (47u) performs the same function in the BITX40 as C52 does in the uBITX.
The interesting thing to note is the presence of D18 (IN4148) in the BITX40, almost exactly as describe your "fix". It is there to block the discharge of this
capacitor onto the RX line.
Thanks for figuring this out !