Late to the party on this one, but a November report from State’s AVC Bureau asserts that

… Burma is in non-compliance with the CWC due to its failure to declare its past chemical weapons (CW) program and destroy its CW production facility (CWPF).  The United States has serious concerns that a CW stockpile may remain at Burma’s historical CW facility.

Moreover, the USG “assesses Burma had a CW program in the 1980s that included a sulfur mustard development program and a CWPF near Tonbo.”  Also, “CW agent and production equipment may remain at Tonbo,” the report says, adding that Myanmar has not declared this facility (among others) to the OPCW.

Here’s more:

…infrastructure has remained at several buildings at the Tonbo site.  Burma has failed to declare four dual-use facilities:  three urea fertilizer plants and a methanol production plant under the Burmese Ministry of Energy which probably have annual production capacities that meet declaration requirements.  The United States is also concerned that Burma did not declare two other locations that may have been involved in Burma’s military-run CW program.  However, most of the original buildings associated with Burma’s legacy research, production, weaponization, and storage of sulfur mustard munitions remain at the historic CWPF near Tonbo, which was Burma’s primary CW research, production, weaponization, and storage center during the 1980s.  The physical integrity of the buildings at Tonbo remain intact.

The report also has a section titled “Efforts to Resolve Compliance Concerns;” I think this is the key takeaway:

Although the civilian government has actively engaged in discussions and indicated its commitment to fulfill its CWC obligations, Burma’s military has not admitted to its past CW program.

The USG reiterated these concerns in November during the most recent conference of CWC States Parties. Here’s Myanmar’s reply:

In its statement, the delegation of the United States of America made reference to my country. In this regard, I would like to make following points: First, Myanmar as a responsible State Party is committed to the earnest implementation of the Convention and strictly adheres to the provisions of the Convention. Second, Myanmar never has an ambition to be a possessor of chemical weapons. Third, Myanmar always puts its utmost efforts for taking measures to be in compliance with the Convention. Fourth, Myanmar is always willing and ready to address any concern raised in this regard in a constructive manner and in accordance with the Convention. Fifth, the Myanmar Government makes sure that coordination among the relevant agencies is led by the National Authority put in place for taking necessary measures accordingly.

The OPCW Implementation report says nothing about the matter.