I do not use Lightroom. There are several version of Lightroom you failed to state which version of Lightroom you have. It is quite possible that version of Lightroom you have installed uses a different version of Adobe RAW Conversion engine then your Photoshop CS5.
The latest version of ACR for CS6 is ACR version 6.7.
Adobe Lightroom does not have ACR support it has its own develop module user interface over Adobe RAW conversion engine. So ACR does not get installed into Lighrroom and the Adobe Raw Conversion engine that Photoshop CS5 ACR 6.7 interfaces with may be a different version then the One the your Lighroom Develop module interfaces with.
It is not clear to me what you doing and seeing.
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