I just found it to be odd that it works, but seems to be working contrary to the laws of digital streams!
I wouldn't assume anything based on the R500 SR lock light and the levels not changing (not sure why they would?). Without further testing - could be a range of causes at this point, we really don't know.
I would test 16/44, 16/48, 24/44 and/or 24/48 output from the UA5 to a device capable of capturing all of the above bit-depth/sample rates and confirm in an audio editor whether the captured streams are, in fact, as expected.
I'd also test the actual content recorded on the R500 to determine whether it is, in fact, 48k, or whether it's actually 44.1k and either <a> the display is wrong, or <b> the WAV header is written incorrectly.
And I'd also try feeding the R500 the same bit-depths/sample rates from another device to see if it behaves the same way.
'Course, that's a fair amount of testing, so if it doesn't really matter to you...