The FT232R breakout board is tiny. It has just the surface mount FT232RL chip itself, and the caps/filters are all within millimeters of it. L1, C1, and C3 are right at the USB connector at the top edge of the chip, but C2 and C5 are a longish way from there.

All of those parts are exactly what FTDI (the chip maker) recommends in their datasheets, but perhaps not quite right for this particular application.

I'll try and work out a metal can or shield for the breakout board, as well as digging out some ceramic discs.

Cheers