This is clearly some kind of an issue with the monitor. People all over the world are having problems with DP connection on the U2414H. Moreover, two professional reviews talk about very strange and absolutely uncommon behavior of the U2414H, when it connected over DP.
TFT Central: On top of this we did find the DisplayPort input to be incredibly fussy. We had a great deal of difficulty getting a laptop connected over DP, when normally on every other screen it's just a simple case of plugging it in and it automatically detecting the appropriate resolution and refresh rate. With the U2414H it seemed to occasionally work, but quite often the screen would inexplicably just show "entering power saving mode" or worse still seem to make the graphics card driver crash when it tried to use DisplayPort. We're not sure what was causing this, but it's the first screen we've used which gave us these kind of issues. From our normal testing PC the DisplayPort to Mini DisplayPort seemed to work fine thankfully. Had the screen featured VGA we could have avoided those issues with the laptop hopefully.
One other issue was that the DisplayPort connections didn't seem to detect a signal if your PC was waking up from sleep, so you'd have to unplug and re-plug the cable sometimes to get the screen to display anything again. Alternatively you can power the screen fully off and on again via the power button which allows it to redetect the input again.
PC Monitors: An Nvidia GTX 780 was used on our test system and we tested both DisplayPort and HDMI – with interesting results. When using either DisplayPort or HDMI the GPU sent out the wrong colour signal (‘Limited Range RGB 16-235’ instead of ‘Full Range RGB 0-255’). This reduced gamma, skewed white point, hugely impacted contrast and simply gave everything a washed out look. We are quite used to seeing this with Nvidia GPUs connected via HDMI as that is their default behaviour – treat the connected device as an HDTV. But we aren’t used to seeing this over DisplayPort which is currently a PC-only output. We tested the ‘MiniDP’ port as well as the full sized DP port using both DP 1.1 and DP 1.2. The native resolution of the monitor (1920 x 1080) is listed under ‘Ultra HD, HD, SD’ as ‘1080p, 1920 x 1080 (native) when connected by DisplayPort. This list of resolutions is designed for output in RGB 16-235 to devices such HDTVs. The resolution should instead be listed under ‘PC’ as ‘1920 x 1080 (native)’, but it isn’t.