Keyframes not placing accurately

When placing, say, a volume keyframe, it will be placed next to the play head instead of on it.

What's the codec and frame rate of the clip, and does it match the frame rate of the timeline? Does it happen with multiple codecs/frame rates or just some? Has any speed effect been applied?

The Clip I tried this on is from a Canon 550D/T2i:-
General
Complete name : M:\Mike and Sharon's Wedding\Canon550D\Card 1 Ceremony and Pics\MVI_6181.MOV
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt 2007.09 (qt /CAEP)
File size : 3.99 GiB
Duration : 12 min 6 s
Overall bit rate : 47.2 Mb/s
Encoded date : UTC 2019-07-24 13:06:30
Tagged date : UTC 2019-07-24 13:06:30
CNDB : ™D

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Baseline@L5
Format settings : 1 Ref Frames
Format settings, CABAC : No
Format settings, Reference frames : 1 frame
Format settings, GOP : M=1, N=12
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 12 min 6 s
Bit rate : 45.6 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Original height : 1 088 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.880
Stream size : 3.86 GiB (97%)
Language : English
Encoded date : UTC 2019-07-24 13:06:30
Tagged date : UTC 2019-07-24 13:06:30
Color range : Full
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.601
Codec configuration box : avcC

Audio
ID : 2
Format : PCM
Format settings : Little / Signed
Codec ID : sowt
Duration : 12 min 6 s
Bit rate mode : Constant
Bit rate : 1 536 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Bit depth : 16 bits
Stream size : 133 MiB (3%)
Language : English
Encoded date : UTC 2019-07-24 13:06:30
Tagged date : UTC 2019-07-24 13:06:30

Timeline Settings.jpg (291.54 KiB) Viewed 582 times

Clip speed is unchanged.

I now believe this to be caused by moving the audio track between milliseconds when snapping is turned off. Keyframes are placed on the millisecond.

For example:-
Here is a 50p clip on a 50p timeline with no changes made to their position.
Opacity and volume keyframes are placed and land in the correct place. (almost lol)

50p Unchanged Audio Track Position.jpg (113.74 KiB) Viewed 582 times

Now the same clip but with the audio shifted between milliseconds.

50p Changed Audio Track Position.jpg (117.55 KiB) Viewed 582 times

Is this normal behaviour? I have no idea.